1969 camaro Z28 backfiring

[Plowman]

Pull the distributor cap off and check for tracking.

[al8apex]

it is a bad condensor in the distributor

[Salvatore]

I would start with:
a plug change
check wires for any arching or wrong firing order
check point dwell
check timing.
may just be a simple plug change.

[wisemanz28]

the cam has under 30,000 miles on it.

[scuncio]

Does the car have the original smog system? I was getting a lean backfire on my old 69 Z until I gutted the original pump.